The present invention relates to compositions and methods of bonding polyester cord tire reinforcement to the butadiene styrene and/or isoprene rubber of the tire carcass and the improved structure obtained thereby.
In the manufacture of polyester cord reinforced tires, the polyester cord usually is uncoated (Greige) or is coated with a polyepoxide by the cord manufacturer which improves adhesion of the polyester cord to the rubbery body of the tire. After the cord is received from the manufacturer in the form of a fabric, the general practice is to prepare the cord by applying a dip coating of a latex. The dip coating of the polyester fabric used in many cases contains a vinyl pyridine/styrene/butadiene terpolymer and a resorcinol-formaldehyde (RF) resin. With Greige polyester cord this dip also contains a high proportion of a resorcinol based specialty resin. While these specialty resins are quite effective in performing their desired function, they are expensive and often unobtainable in the quantities needed. In addition, their composition is a trade secret and it is impossible to reproduce them without knowning the secret. Attempts at making tires without the use of the specialty resins have resulted in poor adhesion of the rubber to the polyester cord, resulting in the rubber being stripped away from the cord in high speed tests.
Materials other than the specialty resins have been used in the prior art to achieve adhesion in special circumstances. For instance in the prior art manufacture of rubber products based upon ethylene copolymers it was found that RF resin gave poor adhesion of the reinforcing cord to the polyethylene rubber. According to U.S. Pat. No. 3,575,792, Blummell, issued 1971, this problem was solved by the addition of a polydiolefin to the ethylene-propylene polymer of his latex cord dip. In addition, the patent appears to disclose that adhesion is improved by the addition of low half-life peroxides to copolymerize the polydiolefin to the ethylene propylene latex of the cord dip. A similar grafting process is disclosed in U.S. Pat. No. 3,427,183 of Portolani 1969.